System and method for downhole gamma ray inspection behind multistring completions

A method for identifying a defect within a multistring wellbore, comprising:

• aligning a scanning tool with a first region of interest of the multistring wellbore;
• obtaining first data corresponding to a first count rate at the first region of interest;
• aligning the scanning tool with a second region of interest of the multistring wellbore;
• obtaining second data corresponding to a second count rate for the second region of interest;
• identifying based at least in part on the first count rate and the second count rate, a defect within at least one of the first region of interest or the second region of interest, the defect being associated with a cement layer of the multistring wellbore that is behind at least one other intermediate layer positioned between the scanning tool and the cement layer.

A downhole logging system, comprising:

• a gamma ray source positioned within a logging tool, the gamma ray source to emit radiation into an area surrounding the logging tool;
• a collimator associated with the gamma ray source, the collimator to adjust an opening to direct a flow of radiation into the formation to permit gamma ray scanning of the formation;
• a radiation detector operable to detect backscatter radiation from the area, the radiation detector associated with an aperture movable to be aligned with the collimator associated with the source;
• and
• a motor to rotate the collimator and the aperture in either a continuous or stepping fashion for scanning a borehole,
• wherein the area includes a multistring completion having at least one casing and at least one cement layer, the logging tool being positioned within a tubular extending into an annulus of the casing.